一种可内生Al2O3扩散障的δ-Ni2Al3-Cr2O3/ Ni-Cr2O3涂层体系

通过对Ni-Cr₂O₃复合镀层620 ℃部分渗铝制备了δ-Ni₂Al₃-Cr₂O₃/Ni-Cr₂O₃涂层体系。Cr₂O₃颗粒在渗铝的过程中和Al反应生成更为稳定的Al₂O₃。1000 ℃恒温氧化20 h后发现,铝化物涂层和复合镀层内掺杂的Cr₂O₃颗粒完全转化为Al₂O₃,并在铝化物涂层/Ni镀层界面自发形成了一层Al₂O₃富集层,该富集层起扩散障作用,阻碍铝化物涂层因互扩散所致的退化。     

Properties of copper matrix reinforced with various size and amount of Al2O3 particles

Copper matrix was reinforced with Al₂O₃ particles of different size and amount by internal oxidation and mechanical alloying accomplished using high-energy ball milling in air. The inert gas-atomised prealloyed copper powder containing 1 wt.% Al as well as a mixture of electrolytic copper powder and 3 wt.% commercial Al₂O₃ powder served as starting materials. Milling of Cu-1 wt.% Al prealloyed powder promoted formation of fine dispersed particles (1.9 wt.% Al₂O₃, approximately 100 nm in size) by internal oxidation. During milling of Cu-3 wt.% Al₂O₃ powder mixture the uniform distribution of commercial Al₂O₃ particles has been obtained. Following milling, powders were treated in hydrogen at 400 °C for 1 h in order to eliminate copper oxides formed at the surface during milling. Compaction was executed by hot-pressing. Compacts processed from 5 to 20 h-milled powders were additionally subjected to high-temperature exposure at 800 °C in order to examine their thermal stability and electrical conductivity. Compacts of Cu-1 wt.% Al prealloyed powders with finer Al₂O₃ particles and smaller grain size exhibited higher microhardness than compacts of Cu-3 wt.% Al₂O₃ powder mixture. This indicates that nano-sized Al₂O₃ particles act as a stronger reinforcing parameter of the copper matrix than micro-sized commercial Al₂O₃ particles. Improved thermal stability of Cu-1 wt.% Al compacts compared to Cu-3 wt.% Al₂O₃ compacts implies that nano-sized Al₂O₃ particles act more efficiently as barriers obstructing grain growth than micro-sized particles. Contrary, the lower electrical conductivity of Cu-1 wt.% Al compacts is the result of higher electron scatter caused by nano-sized Al₂O₃ particles.     

Synthesis of fine composite particles for hydrogen storage, starting from Mg-YNi2 mixture

We synthesized new composite particles for hydrogen storage on the basis of an idea of “particle designing”. As starting materials, powders of Mg and YNi₂ were selected. Fine composite particles containing mainly Mg₂Ni could be designed by repetitive hydriding and dehydriding cycles at 673 K. In the synthesis process of the composite particles, the following two points were found to be essential for this technique. The first point is that, after being activated by the sequential processes of hydrogenation, amorphization and disproportionation, YNi₂ reacts effectively with Mg. The second point is that evaporated Mg, which occurs during dehydriding, adheres to the surface of the activated YNi₂ and accelerates a diffusion reaction to form Mg₂Ni at the interface. In these composite particles, Mg₂NiH₄ is formed, even at 373 K, under a hydrogen pressure of 5 MPa.     

Kinetic and spectral aspects in chemiluminescence system Eu(III)/HCO3/H2O2

Chemiluminescence (CL) of the systems containing Eu₂⁺ or HCO₃⁻ ions and hydrogen peroxide was studied. The kinetic curves and CL emission spectra of the systems were discussed. The emission spectrum of the system containing carbonates revealed two emission maxima: the first directly after initiation of the reaction by hydrogen peroxide and the second in several seconds after the first. On the basis of the characteristic bands in the CL spectrum the emitters in the system Eu₂⁺/HCO₃⁻/H₂O₂ were identified as: excited Eu³⁺ ions and excited products of carbonate decomposition. The emission bands for λ=600 and 420 nm appeared in a time distance of a few ten seconds.     

The oxidation of micro-crystalline Co–Cr alloys under balanced oxygen pressure of Co2O3/Co powders

Surface micro-crystallizing was applied to Co–5Cr, Co–10Cr and Co–15Cr alloys by electro-spark deposition (ESD) and the oxidation behaviors of both cast and micro-crystalline alloys were investigated at 1000 °C under balanced oxygen pressure of Co₂O₃/Co-mixed powders. Surface and cross-section SEM morphologies, EDS and XRD analysis show that micro-crystallizing promotes both the external oxidation and internal oxidation of Co–5Cr alloy. Micro-crystallizing provides more grain boundaries so that the diffusion is enhanced. The inwards diffusion of O makes internal oxidation zone thicker while the outwards diffusion of Cr makes external oxidation more prominent for the micro-crystalline Co–5Cr alloy. For both the cast and micro-crystalline Co–10Cr and Co–15Cr alloys, 10 wt.% Cr is enough to form complex selective oxides (AO/AB₂O₄/BO) scales and 15 wt.% Cr is still not enough to form a single Cr₂O₃ oxide scale. Micro-crystallizing promotes the outwards diffusion of Cr and selective Cr₂O₃ scales are easier to form so that the external oxides scales of micro-crystalline Co–10Cr and Co–15Cr alloy are much thinner and their Cr/Co ratios are higher. The oxidation model of A–B alloy under oxygen pressure that both A and B can be oxidized is also proposed.     

Development of moderate temperature CVD Al2O3 coatings

Chemically vapor deposited Al₂O₃ coatings, due to their high hardness and chemical inertness, are currently the state of art in the cutting tool industry. The conventional high deposition temperature of about 1050 °C for Al₂O₃ coatings, based on the water–gas shift process, has to a great extend restricted the development of several hybrid coatings, such as TiC/TiN/TiCN/Al₂O₃. To overcome this limitation, alternate systems to deposit Al₂O₃ at moderate temperatures have been investigated. Systems using NO–H₂, H₂O₂, NO₂–H₂ and HCOOH were identified and thermodynamic calculations were performed to evaluate them as potential sources of oxygen donors to form Al₂O₃ in the moderate temperature range of 700–950 °C. Preliminary results have clearly demonstrated that it is possible to grow moderate temperature alumina (using such alternate sources) on the TiC/TiN coated cemented carbide substrates.     

封孔处理等离子喷涂Cr2O3涂层耐蚀性的电化学表征

用等离子喷涂工艺在Q235钢基体上制备Cr₂O₃陶瓷涂层,并采用磷酸铝和环氧树脂对其进行封孔处理。利用图像分析法和电化学方法对封孔前后涂层的孔隙率进行了测试,采用弱极化技术和电化学阻抗谱技术对封孔前后涂层的耐蚀性能进行了研究。结果表明,封孔处理提高了涂层的耐蚀性能,环氧树脂封孔涂层的耐蚀性能更优异;陶瓷涂层在腐蚀介质中耐蚀性能主要取决于涂层的孔隙率。     

Fabrication and wear characteristics of MoSi2 matrix composite reinforced by WSi2 and La2O3

MoSi₂ matrix composites (RWM) reinforced by the addition of both WSi₂ and La₂O₃ were fabricated by mechanical alloying and self-propagating high-temperature synthesis (SHS) technique. This composite was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is difficult to synthesize RWM composite by mechanical alloying with Mo–W–Si–La₂O₃ powder mixture, and suitable by self-propagating high-temperature synthesis. The hardness and toughness of MoSi₂ was improved significantly by the addition of both, WSi₂ and La₂O₃ more than by only WSi₂. By adding 0.8 wt.% La₂O₃ and 50 mol.% WSi₂ into the MoSi₂ matrix, this composite has the highest hardness and toughness and exhibits more wear resistance than monolithic MoSi₂ during the sliding wear test under oil lubrication, in this case, the material removal mechanism has been observed to be micro-cutting and micro-fracture.     

Thermal cycle behavior of plasma sprayed La2O3, Y2O3 stabilized ZrO2 coatings

The effects of La₂O₃ addition on thermal conductivity, phase stability and thermal cycle life of Y₂O₃ stabilized ZrO₂ plasma sprayed coatings were investigated. Although low thermal conductivity as well as high resistance to sintering was achieved by La₂O₃ addition, it tended to also result in lower phase stability and thermal cycle life of the coatings. Optimization of the composition and structure of the coatings improved these properties, and the optimized coatings showed prolonged thermal cycle life.     

Hydriding combustion synthesis of Mg–CaNi5 composites

The composites of Mg–x wt.% CaNi₅ (x = 20, 30 and 50) were prepared by hydriding combustion synthesis (HCS) and the phase evolution during HCS as well as the hydriding properties of the products were investigated. It was found that Mg reacted with CaNi₅ forming Mg₂Ni and Ca during the heating period of HCS. Afterwards, the resultant Mg₂Ni and Ca as well as the remnant Mg reacted with hydrogen during the cooling period. The lower platform in the P–C isotherms corresponds to the hydriding of Mg, and the higher one corresponds to Mg₂Ni. With the increase of the content of CaNi₅ from 20 to 50 wt.%, the hydrogen content of the HCS products increases at first and then decreases. The Mg–30 wt.% CaNi₅ composite has the maximum hydrogen capacity of 4.74 wt.%, and it can absorb 3.51 wt.% of hydrogen in the first hydriding process without activation.     

Effects of H2O2 pretreatment on surface characteristics and bioactivity of NaOH-treated NiTi shape memory alloy

The effects of H₂O₂ pretreatment on the surface characteristics and bioactivity of NaOH-treated NiTi shape memory alloy(SMA) were investigated by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, Fourier transform infrared spectroscopy as well as a simulated body fluid(SBF) soaking test. It is found that the H₂O₂ pretreatment can lead to the direct creation of more Ti—OH groups and the decrease in the amount of Ni₂O₃, Na₂TiO₃ and remnant NiTi phases on the surfaces of bioactive NiTi SMA prepared by NaOH treatment. As a result, the induction period of apatite formation is shortened by dispensing with the slow kinetic formation process of Ti—OH groups via an exchange of Na⁺ ions from Na₂TiO₃ phase with H₃O⁺ ions in SBF, which indicates that the bioactivity of NaOH-treated NiTi SMA can be further improved by the H₂O₂ pretreatment.     

Remarkable improvement of hydrogen sorption kinetics in magnesium catalyzed with Nb2O5

Kinetics of hydrogen absorption and desorption reactions was investigated on the MgH₂ composite doped with 1 mol% Nb₂O₅ as a catalyst by ballmilling. The composite after dehydrogenation at 200 °C absorbed gaseous hydrogen of 4.5 mass% even at room temperature under lower pressure than 1 MPa within 15 s and finally its capacity reached more than 5 mass%. On the other hand, the catalyzed MgH₂ after rehydrogenation desorbed 6 mass% hydrogen at 160 °C under purified He flow, which followed the first order reaction. From the Kissinger plot, the activation energy for hydrogen desorption was estimated to be 71 kJ/mol H₂, indicating the product was significantly activated due to the catalytic effect of Nb₂O₅.     

Thermodynamic properties and phase diagrams of the binary systems B2O3–Ga2O3, B2O3–Al2O3 and B2O3–In2O3

We calculated the binary phase diagrams B₂O₃–Ga₂O₃, B₂O₃–In₂O₃ and B₂O₃–Al₂O₃, and the Gibbs energy of formation of the binary compounds, using experimental liquidus data. The B₂O₃–Ga₂O₃ system is of industrial importance, because liquid B₂O₃, in which Ga₂O₃ is not very soluble, is used to protect GaAs during growth of single crystals of GaAs. During recovery of noble metals B₂O₃ is added to slags containing Al₂O₃ to lower the melting point and the viscosity. The B₂O₃–In₂O₃ system is of much less importance to industry. In all three systems we have a liquid miscibility gap, and also solid binary compounds, none of which melt congruently. The miscibility gaps are not surprising, because even in the B₂O₃–Bi₂O₃ system where four congruently melting compounds are present, a liquid miscibility gap exists close to B₂O₃.     

Zur Kenntnis eines gemischtvalenten Lanthanoxovanadats: La11VV3O26

Single crystals of La₁₁V⁴⁺V₃⁵⁺O₂₆ were prepared by high temperature reactions in an N₂/H₂ mixture above the melting point of the initial oxides V₂O₅–La₂O₃. X-ray investigations of the dark blue crystals reveal triclinic symmetry, space group with = 7.088 Å, β = 10.213 Å, χ = 10.250 Å, = 89.59°, β = 71.10°, τ = 70.00°, Z = 1. The lanthanum-rich compound exhibits a new structure type characterized by a complicated La₁₁O₂₆^19- network with incorporated V⁴⁺/V⁵⁺ ions. The VO₄ tetrahedra are isolated from each other and occupied with V⁴⁺ and V⁵⁺ in a statistical manner.

Résumé

Einkristalle von La₁₁V⁴⁺V₃⁵⁺O₂₆ wurden durch Hochtemperaturreaktionen unter N₂/H₂-Mischungen oberhalb des Schmelzpunktes von V₂O₅-La₂O₃ dargestellt. Die röntgenographische Untersuchung der tiefblauen Kristalle führte zu trikliner Symmetrie, Raumgruppe mit = 7,088 Å, β = 10,213 Å, χ = 10,250 Å = 89,59°, β = 71,10°, τ=70,00°, Z = 1. Die lanthanreiche Verbindung bildet einen neuen Strukturtyp und zeichnet sich durch ein kompliziertes La₁₁O₂₆^19- Gerüst aus, in welches V⁴⁺/V⁵⁺-Ionen eingelagert sind. Die gebildeten VO₄-Tetraeder treten zueinander isoliert auf und sind statistisch mit V⁴⁺ und V⁵⁺ besetzt.     

Improvement of the hydrogen-storage kinetics of Mg by reactive mechanical grinding with 10 wt.% Fe2O3 and 5 wt.% Ni

The addition of Fe₂O₃ to Mg is believed to be able to increase the hydriding rate of Mg, and the addition of Ni is thought to be able to increase the hydriding and dehydriding rates of Mg. A sample Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) was prepared by mechanical grinding under H₂ (reactive mechanical grinding). The as-milled sample absorbed 4.61 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min. Its activation was accomplished after two hydriding-dehydriding cycles. The activated sample absorbed 4.59 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min, and desorbed 3.83 wt.% hydrogen at 593 K under 1.0 bar H₂ for 60 min. The activated Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) had a slightly higher hydriding rate at the beginning of the hydriding reaction but a much higher dehydriding rate compared with the activated Mg-10 wt.%Fe₂O₃. prepared via spray conversion. After hydriding-dehydriding cycling, Fe₂O₃ was reduced, Mg₂Ni was formed by the reaction of Mg with Ni, and a small fraction of Mg was oxidized.     

表面活化Al2O3陶瓷与5005铝合金真空钎焊

采用Al-Si钎料对经过Ag-Cu-Ti粉末活性金属化处理的Al₂O₃陶瓷与5005铝合金进行了真空钎焊,研究了钎焊接头的典型界面组织,分析了钎焊温度对接头界面结构特征及力学性能的影响. 结果表明,接头典型界面结构为5005铝合金/α-Al+θ-Al₂Cu+ξ-Ag₂Al/ξ-Ag₂Al+θ-Al₂Cu+Al₃Ti/Ti₃Cu₃O/Al₂O₃陶瓷. 钎焊过程中,Al-Si钎料与活性元素Ti及铝合金母材发生冶金反应,实现对两侧母材的连接. 随着钎焊温度的升高,陶瓷侧Ti₃Cu₃O活化反应层的厚度逐渐变薄,溶解进钎缝中的Ag和Cu与Al反应加剧,生成ξ-Ag₂Al+θ-Al₂Cu金属间化合物的数量增多,铝合金的晶间渗入明显;随钎焊温度的升高,接头抗剪强度先增加后降低,当钎焊温度为610 ℃时,接头强度最高达到15 MPa.     

Structure and hydrogen storage properties of MgH2 catalysed with La2O3

The catalytic effect of the addition of lanthanum oxide (La₂O₃), in the range 0.5–2.0 mol%, on the hydrogen storage properties of MgH₂ prepared by ball milling has been studied. The addition of La₂O₃ reduces the formation during milling of the metastable orthorhombic γ-MgH₂ phase. The desorption rate of samples with 1 and 2 mol% La₂O₃ comes out to be about 0.010 wt% per second at 573 K under an hydrogen pressure of 0.3 bar, better than for sample with 0.5 mol% La₂O₃. The presence of LaH₃ after hydrogenation/dehydrogenation cycles has been observed in all samples. The sample with 1 mol% of La₂O₃ gives a lower hysteresis factor compared with sample with 2 mol%.     

Nb–20%Ta alloy powder by the hydriding–dehydriding technique

Nb–Ta alloys have been used in the chemical industry to substitute pure Ta in corrosive environments (inorganic acids at high temperature). The production of components from these alloys does not show important technical problems due to the high ductility of these materials. The present work is aimed at the production of Nb–20%Ta (wt%) alloy powders by the hydriding–dehydriding technique. The alloy was produced in ingot form by the aluminothermic reduction of oxides (Nb₂O₅/Ta₂O₅) and electron beam melting. The hydriding step has been carried out in a hydrogen gas atmosphere at different temperatures using chips machined from the ingot. No significant hydriding has been observed in the experiments carried out below 500 °C, meaning that it is the lowest possible hydriding temperature of the material through the adopted experimental procedure. The XRD patterns of the hydride and Nb–20%Ta powders coincide with those of β-NbH_0.89 and Nb XRD standards, respectively. The powders were of angular and irregular morphology. The specific masses of the hydride and Nb–20%Ta powder were determined as approximately 8.55 and 9.57 g/cm³, respectively. The apparent and TAP specific masses of the hydride and Nb–20%Ta powders were (4.30/5.60) and (4.65/6.10) g/cm³, respectively.     

Al2O3/TiB2/Al复合材料的微观结构和高温力学性能

以细雾化铝粉和TiB₂颗粒为原料,通过粉末冶金和热轧制制备微米TiB₂和纳米Al₂O₃颗粒增强铝基复合材料。室温时,由于TiB₂和Al₂O₃的综合强化作用,Al₂O₃/TiB₂/Al复合材料的屈服强度和抗拉强度分别为258.7 MPa和279.3 MPa,测试温度升至350℃时,TiB₂颗粒的增强效果显著减弱,原位纳米Al₂O₃颗粒与位错的交互作用使得复合材料的屈服强度和抗拉强度达到98.2MPa和122.5 MPa。经350℃退火1000 h后,由于纳米Al₂O₃对晶界的钉扎作用抑制晶粒长大,强度和硬度未发生显著的降低。     

钕的添加对V2O5-MoO3/TiO2平板式脱硝催化剂性能的影响

本研究制备了一系列不同Nd含量的V₂O₅-MoO₃-Nd₂O₃/TiO₂平板式脱硝催化剂。采用XRD、N2-吸附脱附、XPS、H2-TPR、拉曼光谱、NH3-TPD和红外光谱等表征手段对催化剂进行分析。结果表明:适量的Nd2O3(0.25%、0.5%,质量分数)可以增强V₂O₅-MoO₃/TiO₂催化剂的还原性能,增加了催化剂的Oα/(Oα+Oβ)比率,从而提升了催化剂的脱硝活性。然而,过量Nd₂O₃(0.75%、1%)的添加,会导致催化剂酸性性能的显著降低,造成催化剂脱硝性能的下降。此外,过量Nd的添加还会对催化剂的耐磨性能有负面影响。各催化剂中,VMoN d(0.5%)/Ti催化剂显示了最佳的脱硝活性。并且,该催化剂还显示了优良的抗SO₂、H₂O性能。